docs: def wav_length(fn: str) -> float:
      """ Returns the length of the WAV file in seconds."""
  
      args = [config.SOX_PATH, fn, "-n", "stat"]
      p = subprocess.Popen(
          args, stdin=PIPE, stdout=PIPE, stderr=PIPE)
      length_line = str(p.communicate()[1]).split("\\n")[1].split()
      print(length_line)
      assert length_line[0] == "Length"
      return float(length_line[-1])